Cardiac pacemakers generally provide functions including sensing electrical signals generated by the heart, controlling stimulation of excitable tissues in the heart, sensing the response of the heart to such stimulation, and responding to inadequate or inappropriate stimulus or response (e.g., dysrhythmia) to deliver therapeutic stimuli to the heart. Some existing cardiac pacemakers also function to communicate with an external programmer device to support a variety of monitoring, diagnostic and configuration functions.
Certain cardiac pacemakers include an internal accelerometer for measuring the level of activity of the patient (e.g., movement caused by walking around, or by muscle twitches). Such pacemakers process (e.g., filter) the accelerometer signals to reduce noise interfering with the measurement of the patient's activity, such as the sounds generated by the heart itself, and then use the processed signals as inputs to algorithms for generating the signals used to control the stimulation of the heart. For example, if accelerometer signals indicate that a patient is walking briskly, the pacemaker may stimulate the heart to beat at a faster rate (often subject to an upper rate limit) than when the patient is at rest. While the accelerometer signal is used internally to control the heart rate, this signal is not transmitted by the pacemaker to an external programmer for subsequent display on a display device. Thus, the accelerometer signal itself is an internal signal which is not output to the user.
A common method of diagnosing heart problems involves comparing the electrical operation of the heart to its mechanical operation, and identifying electrical-mechanical disassociation. Typically, a physician listens to a patient's heart using a stethoscope placed on the surface of the patient's body, and compares the heart sounds to an electrocardiograph (ECG) trace generated by an ECG machine coupled to probes placed on the patient's chest. This method suffers from several disadvantages, including the need to use the stethoscope, the effect of various factors (e.g., the placement of the stethoscope, body fat, etc.) on the heart sounds, the need to electrically couple ECG probes to the patient's chest, the difficulties faced by the physician in accurately comparing the sounds heard using the stethoscope to the traces displayed by the ECG machine, and the relatively high level of skill needed to perform this comparison (especially if a physician is not available). This method also does not continuously monitor for electrical-mechanical disassociation, thus making it difficult to detect disassociation occurring between visits to the physician, and does not provide the ability to produce a written record showing a detected disassociation.
Thus, it would be desirable to provide a method and apparatus for outputting heart sounds, and/or for comparing electrical operation of the heart to mechanical operation of the heart, that overcome one or more of the above-described disadvantages.